1. Field of the Invention
This invention relates to valve-gated injection molding systems and, in particular, those systems in which an actuator is positioned laterally from an injection nozzle body.
2. Related Art
Valve-gated injection molding systems conventionally include a valve pin disposed in a nozzle melt channel. The valve pin extends through the manifold melt channel to a double acting air-operated piston which moves the valve pin into and out of a position that blocks the nozzle outlet. Such a conventional system can be seen, for example, in U.S. Pat. No. 4,173,448 to Rees et al. and in FIG. 8 of the drawings provided herewith. In this type of conventional system, the actuator is mounted in a plate upstream of the manifold. Such a conventional system has certain disadvantages. For example, the actuator located on top of the manifold increases the height of the overall system. Further, the valve pin is long, which increases the risk of breakage, bending, and/or misalignment within the melt channel. Still further, because the valve pin extends through the heated nozzle and the heated manifold, it is exposed to the expansion and contraction and relative movement of those parts. This further increases the risk that the valve pin may bend or become misaligned in the melt channel. Further, in systems with a large amount of mold cavities, there is greater risk of inconsistency between the different valve pins due to this bending or misalignment. Another problem with this type of valve-gated injection molding system is that melt from the manifold melt channel tends to leak up towards the piston assembly. Seals are required around the valve pin above the manifold to stop the leakage.
Other conventional systems attempt to address some of these problems. For example, U.S. Pat. No. 4,919,606 to Gellert discloses a valve-gated injection molding system wherein a cylinder and piston assembly is located to a side of the manifold. The movement of the piston is translated to the valve pin through a rack and pinion arrangement. This type of arrangement addresses the height of the overall system and the length of the valve pins. However, this system is expensive to manufacture as it uses highly accurate components. Other similar systems also move the piston assembly adjacent to the manifold or the nozzle and translate the movement of the piston laterally to actuate the valve pin, such as in shown in U.S. Pat. Nos. 5,902,614; 5,916,605; and 5,984,661. These types of arrangements suffer from difficulty in transferring axially the necessary force from the piston assembly to the valve pin. They also include bends in the nozzle melt channel that are not heated in order to allow access to the valve pin from a lateral position.
Another conventional system includes an annular slidable piston member which surrounds the nozzle and is known as an “in-line annular piston valve gated nozzle”. Due to a connection between a slidable member and a valve pin, vertical motion of the slidable member causes the vertical motion of the valve pin. Such a system can be seen in U.S. Pat. Nos. 3,677,682 and 6,159,000, for example. In such systems, the slidable member is often too close to the nozzle body and is therefore subject to high temperatures which can degrade components thereof, such as annular sealing members (i.e. O-ring seals). Also, many of such systems are complicated and/or expensive to manufacture and require the use of special heat resistant materials. Furthermore, many of such systems do not have heaters or heater components for applying heat to that portion of the melt channel around which the slidable member is slidable. In those systems which do have heaters for heating such a portion of the melt channel, the heaters are often not evenly radially spaced from the melt channel, i.e. are asymmetrical relative to the melt channel, thereby resulting in either too much or too little heat being applied to melt flowing therethrough.